The Universe

Dark Matter and Dark Energy

Have astronomers determined the matter and energy density of the universe?

Based on measurements of the gravitational effects of dark matter and luminous matter in the distant universe, astronomers have measured Ω (that is, ΩDM ΩB) to be about 0.3. Meanwhile, based on detailed observations of distant Cepheid variables and Type Ia supernovae, astronomers have deduced that the expansion rate of the universe is increasing. That means that Λ is greater than zero. Finally, based on careful study of the cosmic microwave background, astronomers have confirmed that the universe has a flat geometry, meaning that Ω Λ = 1. Carrying the precision of these measurements to one decimal place, the current measurements show that Ω = 0.3 and Λ = 0.7. If these numbers hold true, then our universe is destined to expand forever and there will be no Big Crunch.